1. Field of the Invention
The present invention relates to medical apparatus and more particularly to electroconvulsive therapy apparatus.
2. Description of the Related Art
Electroconvulsive therapy ("ECT"), sometimes called "shock therapy", is frequently used to treat major depression. A report of a NIMH panel (National Institute of Mental Health), reported in Science (June 28, 1985, pg. 1510, 1511), concluded that "not a single controlled study has shown another form of treatment to be superior to ECT in the short-term management of severe depressions." The Science article noted that the complication rate is about 1 in 1700 treatments and severe and prolonged memory loss is extremely rare, and possibly non-existent.
In electroconvulsive therapy (ECT) generally two electrodes are applied to the forehead of the patient, one on the left and the other on the right side. An electric current is applied between the two electrodes on the forehead. A small portion of the current reaches the brain, the rest being deflected by the skin and skull.
In the "Thymatron" ECT instrument (TM of Somatics, Inc., Lake Bluff, Illinois) the stimulus is a brief series of electrical square waves. The stimulus is a constant current of 0.9 amps limited to 450 volts, consisting of 140 bipolar pulses per second of 1 msec. width, which is adjustable 0.2-4.0 seconds in duration.
The physician determines the length of the applied electricity, taking into account such factors as the patient's age, size, physical condition and prior history of electroconvulsive therapy. The physician may, with presently available apparatus, reasonably accurately select the desired electrical duration.
The ECT therapy is based upon inducing an electrical response in the neural tissue of the patient's brain. This appears on an electroencephalograph (EEG) instrument, using analog printed wavy lines, as a pattern similar to a typical epileptic grand mal seizure pattern. It is believed that the therapeutic benefit of the ECT is primarily due to the induced seizure.
It has recently been recognized that when administering ECT it is important for the physician to monitor the brain's electrical activity to determine both the occurrence and the duration of the induced seizure (National Institutes of Health, Consensus Conference, Electroconvulsive Therapy, J.A.M.A. 254:2103-2108, 1985). An electrical stimulus that does not induce a seizure, or one that induces a seizure of insufficient duration (e.g., less than 25 seconds) is not considered to have any therapeutic effect. The treatment must be repeated with a larger electrical dosage, i.e. generally a greater electrical charge, to try to induce a seizure expected to be of full therapeutic benefit to the patient. On the other hand, a seizure that is too long (e.g., longer than 3 minutes) may cause excessive memory impairment in the patient, or require more intensive supervision of the patient during and after the treatment. It is customary medical practice to immediately terminate such prolonged seizures by administration of suitable anticonvulsant agents according to the physician's judgment.
The existing methods used to monitor the electrical activity of the brain during ECT are based on conventional EEG technology. Generally an EEG device is used to amplify the patient's brain waves, filter the amplified brain wave signals to remove muscle artifact and ambient electrical noise, display the brain wave activity in the form of wavy lines on paper or lines on an oscilloscope screen, or similarly fluctuating audible tones played through an audible speaker. The physician may then judge the occurrence of the seizure by interpreting the paper EEG record, oscilloscope display, or auditory EEG signal. He then makes a determination of the length of the seizure by further interpreting the particular representation of the EEG signal, thereby a spike-like form on an EEG graph, while simultaneously viewing a timepiece. However, judgments based on interpretations of the visual, or auditory, EEG signals require special medical expertis and familiarity with EEG patterns that typically occur during ECT. Such judgments are necessarily subjective, rely on the attention and experience of the physician, and have been reported in the medical literature to be unreliable (Ries, R.K., Biol. Psychiat. 20:94-119, 1985). Moreover, to determine the duration of the seizure, the physician must attend to the visual, or auditory, representation of the EEG signal, as well as to a separate timepiece, just when his attention is urgently required to observe the patient undergoing the seizure.